Frequency changer



1932- c. w. HANSELL 1,874,982

FREQUENCY CHANGER Filed June 20, 1929 In J 5 M.

INVENTOR CLARENCE W. HANSELL Aowv/ ATTORNEY Patented Aug. 30, 1932 UNITED STATES PATENT, OFFICE CLARENCE W. HANSELL, 0F PORT JEFFERSON, NEW YORK, ASSIGNOR 1'0 RADIO OOBI O- BATION OF AMERICA, A CORPORATION OF DELAWARE V rnnounnov omens.

Application filed June 20, 1929. Serial No. 872,237.

This invention relates to a frequency changer and especially to new and useful methods and means for varying the frequency at which a' piezo-electric crystal vibrates.

Heretofore, frequency variation in a crystal was accomplished by varying the tuning of the circuits with which the crystal was associated, or by varying the air gaps about one or more faces of the crystal. latter case variation of the gap causes a variation in the natural period of the column of medium in contact with aface of the crystal, thereby varying the crystal frequency.

According to this invention the dimensions of the media in contact with one or more faces of the crystal are kept constant; but, by varying the pressure or stiffness of the media, the crystal frequency is changed in any desired fashion. The resulting electrical vibrations are utilized in any desired manner such as,for example, wobbling the" frequency of a transmitter in order to reduce fading effects at a receiver, or for frequency modulation.

In one embodiment of my invention a crystal has in contact with one or more of its faces a column of air of a length such that its natural period differs slightly from that of the crystal. Because of this, the crystal will tend to vibrate at some frequency intermediate is own and that of the column of air. By varying the pressure of the air column the reaction on the crystal is varied and hence the frequency of vibration of the crystal is also changed.

The changes in pressure in the air column I cause, in any suitable fashion, for example, by means of a vibrating diaphragm, vibrating in a predetermined fashion. However, if the crystal is not suitably mounted reflections in the pressure waves produced in the column of air may aifect in any undesirable manner, the frequency of vibration of the crystal; and, in order to avoid these undesirable reflections I provide, according to my invention, means, in connection with the means for causing the pressure waves, for preventing these reflections and for conduct- In the I ing the pressure waves unidirectionally across a surface or surfaces of the crystal.

Further in accordance with this invention I provide means whereby pressure waves may be applied to crystal faces either in phase or m oppos1te phase relationship in order to assist and emphasize frequency change in the cr stal.

n accordance with the practice of the United States Patent Oflice, the novel features of my invention are defined in the appended claims; however, my invention may best be understood, both as to its structure and method of operation, by referring to the accompanying drawing in which F1 ure 1 is a diagrammatic cross-sectional showing of apparatus illustrating a new and improved method for varying the oscillation frequency of a piezo-electric crystal, and

Figure 1a is a cross-section view extending through the crystal and both electrodes of Figure 1 along the line a-a.

' Figure 2 is another embodiment thereof wherein pressure waves of differing phase relationship are applied to surfaces of a crystal for varying its period of vibration.

Figure 2b is a cross-section view extending through the crystal and both electrodes of Figure 2 along the line b-b.

Turning to Figure 1, I have shown a crystal 2 mounted between two spaced members 4, 6 in a manner such that there are air gaps 8, 10 facing surfaces 12, 14 of the crystal. Air gaps or columns 8, 10 may be made equal for this particular arrangement and should be adjusted so as to have a frequency difi'ering slightly from that of crystal 2. Preferably the resonance frequencies of the crystal and the air gaps should be different but their resonance curves should overlap when it is desired to make the crystal oscillation frequency most sensitive to air pressure.

The crystal may be supported in any suitable fashion; thus, it may be bevelled at its ends and supported by elements 16, 18 attached to rods 20, 22 which in turn are fixed to conduits 24, 26 attached in any suitable way to members 4, 6.

A diaphragm 28 is attached at one end in any suitable fashion to conduit 24 and is r vibrated by electromagnet which may be.

preventing reflection and its concomitant i effects.

In the absence of exciting currents for vibrating diaphragm 28 the crystal will vibrate at some frequency intermediate its own'natural frequency and that of the columns of The amount with which the frequency of the crystal will be modified by the use'of the air gaps will depend upon the reaction of the air in the gap upon the crystal. Hence, it will be seen, by varying the pressure of the air in the gaps the reaction can be varied and hence the crystal frequency will be varied in a predetermined fashion, according to the vibration of diaphragm 28. In this manner a crystal disposed .so as to have constant dimensional media contacting with at least one of its faces, is made to have its period of vibration varied according to the stiffness or pressure of the media.

The electrical connections between the faces 12, 14 of the crystal, and the electrical circuits with which the crystal is used, are made through the dielectric capacity of the a1r gaps. Thus the air gaps form series condensers which readily pass electrical currents of the frequencies corresponding to the oscillating frequencies of the crystal. If desired, the crystal may, by means of electrodes 4 and 6 and conductors 50 and 52, be connected to a suitable source ofhigh frequency for modulatin I purposes.

11 Figure 2 I have shown apparatus for unidirectionally passing over a crystal, pressure waves differing in phase. Within a conduit 32 I mount a crystal 34 supported in a similar manner to that shown in Figure 1, at its front and rear faces. Conduit 32 is closed off by a member 36 and between 36 and the crystal 34 there is placed, as shown, a piston 38 vibratable or oscillatable in any desired'fashion by means of rod 40. Conduit 26 in Figure 2 is also exponential in form in order to carry pressure waves unidirectionally thereby preVenting reflection.

In this case, however, the columns 42,44 of media contactin with faces 46, 48 of crystal 34, have di erent dimensions. Column 42 is made to have a natural period of oscillation a little longer than the natural peif the natural frequencies of faces of the crystal are over the'surfaces of crystal 34' riod of oscillation of crystal 34;. whereas, col-' umn 44 is given a natural period ofoscillation alittle less than that of crystal The differences in dimensions of the columns or gaps of air colitactin with the crystal, are necessary because 0 the phase relationshi of the pressure waves ap lied thereto. us, for a given movement 0 piston 38 the pressure waves on faces 48, 46 will be opposite in phase, for example, if there is a compression wave on 48 there is a rarefaction wave on 46.

By the choice of columns having natural tunings on opposite sides of the natural crystal tuning, the effect of res-sure waves for changing the frequency 0 the crystal by the movementof 38 is emphasized; whereas, the aps were taken on one side of the crystal requency, say, both less than the crystal frequency, then the effect of the compression and rarefaction waves would be to neutralize each other and have little frequency.

The rod 40 may,

or no effect on the crystal for example, be moved by'means of an electrom'agnet or by suitably attaching it to a loud speaking telephone unit 70. It is to be distinctly understood, of course, that this invention is not limited to the apparatus as shown in the drawin since an suitable equipment for moving r0 40 may e utilized. The apparatus shown in Figure 2 is as well adapted for use as the apparatus in Figure 1 for either frequency wobbling or for frequency modulation. In Figure 2 also it is clear that, as in Fi re 1, the dimensions of the columns of med1a contacting with sur-- not varied to cause changesin the crystal frequency; but, the stifi'ness or pressure of the media is varied to cause the desired frequencychange. Many changes may obviously be made from the apparatus as shown in the drawin s; and hence, I do not intendto be limited t ereby, but solely by the width of the appended claims.

Having I claim is:

1. The method of varying the natural frequency at which. a piezo-electric crystal vibrates in order to obtain frequency modulated energy which includes contmuously varying the pressure of the medium surroundin the crystal in accordance with signal mod ated energy.

2. The method of varying the natural frequency at which a piezo-electric: crystal vibrates in order to obtain frequency moduthus described my invention, what lated energy which includes continuously varying the pressure of the air surrounding the crystal in accordance lated energy.

3. The method of varying the natural frequency at which a piezo-electric crystal viwith signal moduto have a'gap over one of its faces and means for varying the pressure of the media within the gap without altering the dimensions of the gap.

6. A. crystal having an air gap over one of its faces, and means for varying the pressure of the air in the gap without changing the dimensions of the gap.

7 The method of varying the natural frequency at which a crystal vibrates in apparatus wherein the crystal is mounted between gaps of constant dimensions, which includes subjecting the media in the gaps to pressure waves.

8. The method of varying the natural frequency at which a crystal vibrates in order to obtain frequency modulated energy which includes continuously passing pressure waves unidirectionally over the crystal in accordance with signal modulated energy.

9. In combination, a crystal, means for generating pressure waves and means for causing the generated waves to pass unidirectionally over the crystal in order to vary the natural frequency at which the crystal vibrates.

10. In combination, a crystal, means for producing pressure waves in the media around the crystal and means for conducting the waves through the media and over the crystal without reflection.

11. Apparatus for varying in a predetermined fashion the frequency of vibration of an oscillator comprising a crystal, means for mounting the crystal so that the crystal has air columns over a plurality of its faces, the air columns having natural frequencies differing slightly from the natural frequency of the crystal, and means for varying the pressure of the air columns without changing their dimensions, thereby altering the frequency of vibration of the crystal.

CLARENCE W. HANSELL. 

